The following documents and standards descriptions are hereby incorporated into the present disclosure as if fully set forth herein: i) 3GPP Technical Specification No. 36.211, version 8.8.0, “E-UTRA, Physical Channels and Modulation,” September 2009 (hereafter “REF1”); ii) 3GPP Technical Specification No. 36.212, version 8.8.0, “E-UTRA, Multiplexing And Channel Coding,” December 2009, (hereafter “REF2”); iii) 3GPP Technical Specification No. 36.213, version 8.8.0, “E-UTRA, Physical Layer Procedures,” September 2009, (hereafter “REF3”); iv) Document No. R1-102578, “Way Forward on UL Power Control with Carrier Aggregation,” 3GPP RAN1#60bis, April 2010; and RAN1#60bis—Chairman's note.
Sounding reference signal (SRS) transmission methods are discussed in Release 8 (Rel-8) of the 3GPP Standard in the LTE references REF1, REF2 and REF3 above. A sounding reference signal is transmitted in the uplink from a mobile station to a base station. The base station uses the SRS to determine the characteristics of the channel from the mobile station to the base station.
The base station configures the mobile station to periodically transmit an SRS by radio resource control (RRC) layer signaling. The RRC signaling configures, for example, the period of the SRS transmitted by the mobile station and the resources used (e.g., subcarriers, time slots, cyclic shift, etc.). In Release 8, a sounding reference signal is periodically transmitted by the mobile station on the last single carrier frequency division multiplexing (SC-FDM) symbol in a specifically configured subframe. The power level for SRS SC-FDM symbols may be different (offset) from the power level in physical uplink shared channel (PUSCH) SC-FDM symbols.
However, in Release 10 of the Long Term Evolution Advanced (LTE-A) standard, which is a candidate 4G system to be incorporated in the 3GPP LTE standard, it is proposed that SRS transmissions be performed aperiodically in response to a trigger message transmitted by a base station.
Therefore, there is a need in the art for improved apparatuses and methods for transmitting sounding reference signals aperiodically from a mobile station to a base station. In particular, there is a need for improved apparatuses and methods for configuring the bandwidth and the transmit power levels of the aperiodically transmitted sounding reference signals.